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updated README markdown, gitignore, added the Makefile and fixed weird comments in test.c
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.gitignore
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a.out
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.svn
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*.o
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Makefile
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Makefile
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all: cJSON.o
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cc -Wall cJSON.c -c -o cJSON.o
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cc -Wall cJSON.o test.c -lm
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191
README.md
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README.md
@ -21,6 +21,7 @@
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*/
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Welcome to cJSON.
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-----------------
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cJSON aims to be the dumbest possible parser that you can get your job done with.
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It's a single file of C, and a single header file.
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@ -29,68 +30,68 @@ JSON is described best here: http://www.json.org/
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It's like XML, but fat-free. You use it to move data around, store things, or just
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generally represent your program's state.
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First up, how do I build?
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Add cJSON.c to your project, and put cJSON.h somewhere in the header search path.
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For example, to build the test app:
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gcc cJSON.c test.c -o test -lm
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./test
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gcc cJSON.c test.c -o test -lm
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./test
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As a library, cJSON exists to take away as much legwork as it can, but not get in your way.
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As a point of pragmatism (i.e. ignoring the truth), I'm going to say that you can use it
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in one of two modes: Auto and Manual. Let's have a quick run-through.
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I lifted some JSON from this page: http://www.json.org/fatfree.html
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That page inspired me to write cJSON, which is a parser that tries to share the same
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philosophy as JSON itself. Simple, dumb, out of the way.
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Some JSON:
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{
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"name": "Jack (\"Bee\") Nimble",
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"format": {
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"type": "rect",
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"width": 1920,
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"height": 1080,
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"interlace": false,
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"frame rate": 24
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----------
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{
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"name": "Jack (\"Bee\") Nimble",
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"format": {
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"type": "rect",
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"width": 1920,
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"height": 1080,
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"interlace": false,
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"frame rate": 24
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}
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}
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}
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Assume that you got this from a file, a webserver, or magic JSON elves, whatever,
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you have a char * to it. Everything is a cJSON struct.
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Get it parsed:
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cJSON *root = cJSON_Parse(my_json_string);
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cJSON *root = cJSON_Parse(my_json_string);
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This is an object. We're in C. We don't have objects. But we do have structs.
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What's the framerate?
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cJSON *format = cJSON_GetObjectItem(root,"format");
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int framerate = cJSON_GetObjectItem(format,"frame rate")->valueint;
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cJSON *format = cJSON_GetObjectItem(root,"format");
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int framerate = cJSON_GetObjectItem(format,"frame rate")->valueint;
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Want to change the framerate?
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cJSON_GetObjectItem(format,"frame rate")->valueint=25;
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cJSON_GetObjectItem(format,"frame rate")->valueint=25;
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Back to disk?
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char *rendered=cJSON_Print(root);
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char *rendered=cJSON_Print(root);
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Finished? Delete the root (this takes care of everything else).
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cJSON_Delete(root);
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cJSON_Delete(root);
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That's AUTO mode. If you're going to use Auto mode, you really ought to check pointers
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before you dereference them. If you want to see how you'd build this struct in code?
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cJSON *root,*fmt;
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root=cJSON_CreateObject();
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cJSON_AddItemToObject(root, "name", cJSON_CreateString("Jack (\"Bee\") Nimble"));
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cJSON_AddItemToObject(root, "format", fmt=cJSON_CreateObject());
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cJSON_AddStringToObject(fmt,"type", "rect");
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cJSON_AddNumberToObject(fmt,"width", 1920);
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cJSON_AddNumberToObject(fmt,"height", 1080);
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cJSON_AddFalseToObject (fmt,"interlace");
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cJSON_AddNumberToObject(fmt,"frame rate", 24);
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cJSON *root,*fmt;
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root=cJSON_CreateObject();
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cJSON_AddItemToObject(root, "name", cJSON_CreateString("Jack (\"Bee\") Nimble"));
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cJSON_AddItemToObject(root, "format", fmt=cJSON_CreateObject());
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cJSON_AddStringToObject(fmt,"type", "rect");
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cJSON_AddNumberToObject(fmt,"width", 1920);
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cJSON_AddNumberToObject(fmt,"height", 1080);
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cJSON_AddFalseToObject (fmt,"interlace");
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cJSON_AddNumberToObject(fmt,"frame rate", 24);
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Hopefully we can agree that's not a lot of code? There's no overhead, no unnecessary setup.
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Look at test.c for a bunch of nice examples, mostly all ripped off the json.org site, and
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@ -111,18 +112,20 @@ Sibling hs type False, name "interlace", and a sibling:
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Sibling has type Number, name "frame rate", value 24
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Here's the structure:
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typedef struct cJSON {
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struct cJSON *next,*prev;
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struct cJSON *child;
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---------------------
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int type;
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typedef struct cJSON {
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struct cJSON *next,*prev;
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struct cJSON *child;
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char *valuestring;
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int valueint;
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double valuedouble;
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int type;
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char *string;
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} cJSON;
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char *valuestring;
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int valueint;
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double valuedouble;
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char *string;
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} cJSON;
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By default all values are 0 unless set by virtue of being meaningful.
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@ -146,59 +149,59 @@ the root object, and traverse the structure (which is, formally, an N-tree),
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and tokenise as you please. If you wanted to build a callback style parser, this is how
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you'd do it (just an example, since these things are very specific):
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void parse_and_callback(cJSON *item,const char *prefix)
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{
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while (item)
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{
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char *newprefix=malloc(strlen(prefix)+strlen(item->name)+2);
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sprintf(newprefix,"%s/%s",prefix,item->name);
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int dorecurse=callback(newprefix, item->type, item);
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if (item->child && dorecurse) parse_and_callback(item->child,newprefix);
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item=item->next;
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free(newprefix);
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}
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}
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void parse_and_callback(cJSON *item,const char *prefix)
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{
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while (item)
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{
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char *newprefix=malloc(strlen(prefix)+strlen(item->name)+2);
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sprintf(newprefix,"%s/%s",prefix,item->name);
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int dorecurse=callback(newprefix, item->type, item);
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if (item->child && dorecurse) parse_and_callback(item->child,newprefix);
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item=item->next;
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free(newprefix);
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}
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}
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The prefix process will build you a separated list, to simplify your callback handling.
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The 'dorecurse' flag would let the callback decide to handle sub-arrays on it's own, or
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let you invoke it per-item. For the item above, your callback might look like this:
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int callback(const char *name,int type,cJSON *item)
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{
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if (!strcmp(name,"name")) { /* populate name */ }
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else if (!strcmp(name,"format/type") { /* handle "rect" */ }
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else if (!strcmp(name,"format/width") { /* 800 */ }
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else if (!strcmp(name,"format/height") { /* 600 */ }
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else if (!strcmp(name,"format/interlace") { /* false */ }
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else if (!strcmp(name,"format/frame rate") { /* 24 */ }
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return 1;
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}
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int callback(const char *name,int type,cJSON *item)
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{
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if (!strcmp(name,"name")) { /* populate name */ }
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else if (!strcmp(name,"format/type") { /* handle "rect" */ }
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else if (!strcmp(name,"format/width") { /* 800 */ }
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else if (!strcmp(name,"format/height") { /* 600 */ }
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else if (!strcmp(name,"format/interlace") { /* false */ }
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else if (!strcmp(name,"format/frame rate") { /* 24 */ }
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return 1;
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}
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Alternatively, you might like to parse iteratively.
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You'd use:
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void parse_object(cJSON *item)
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{
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int i; for (i=0;i<cJSON_GetArraySize(item);i++)
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{
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cJSON *subitem=cJSON_GetArrayItem(item,i);
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// handle subitem.
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}
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}
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void parse_object(cJSON *item)
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{
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int i; for (i=0;i<cJSON_GetArraySize(item);i++)
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{
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cJSON *subitem=cJSON_GetArrayItem(item,i);
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// handle subitem.
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}
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}
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Or, for PROPER manual mode:
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void parse_object(cJSON *item)
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{
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cJSON *subitem=item->child;
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while (subitem)
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{
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// handle subitem
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if (subitem->child) parse_object(subitem->child);
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subitem=subitem->next;
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}
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}
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void parse_object(cJSON *item)
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{
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cJSON *subitem=item->child;
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while (subitem)
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{
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// handle subitem
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if (subitem->child) parse_object(subitem->child);
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subitem=subitem->next;
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}
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}
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Of course, this should look familiar, since this is just a stripped-down version
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of the callback-parser.
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@ -212,20 +215,20 @@ You can, of course, hand your sub-objects to other functions to populate.
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Also, if you find a use for it, you can manually build the objects.
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For instance, suppose you wanted to build an array of objects?
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cJSON *objects[24];
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cJSON *objects[24];
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cJSON *Create_array_of_anything(cJSON **items,int num)
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{
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int i;cJSON *prev, *root=cJSON_CreateArray();
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for (i=0;i<24;i++)
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{
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if (!i) root->child=objects[i];
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else prev->next=objects[i], objects[i]->prev=prev;
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prev=objects[i];
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}
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return root;
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}
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cJSON *Create_array_of_anything(cJSON **items,int num)
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{
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int i;cJSON *prev, *root=cJSON_CreateArray();
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for (i=0;i<24;i++)
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{
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if (!i) root->child=objects[i];
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else prev->next=objects[i], objects[i]->prev=prev;
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prev=objects[i];
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}
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return root;
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}
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and simply: Create_array_of_anything(objects,24);
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cJSON doesn't make any assumptions about what order you create things in.
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@ -235,7 +238,6 @@ of those objects.
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As soon as you call cJSON_Print, it renders the structure to text.
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The test.c code shows how to handle a bunch of typical cases. If you uncomment
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the code, it'll load, parse and print a bunch of test files, also from json.org,
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which are more complex than I'd care to try and stash into a const char array[].
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@ -243,5 +245,4 @@ which are more complex than I'd care to try and stash into a const char array[].
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Enjoy cJSON!
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- Dave Gamble, Aug 2009
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4
test.c
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test.c
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cJSON_AddFalseToObject (fmt,"interlace");
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cJSON_AddNumberToObject(fmt,"frame rate", 24);
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out=cJSON_Print(root); cJSON_Delete(root); printf("%s\n",out); free(out); /* Print to text, Delete the cJSON, print it, release the string.
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out=cJSON_Print(root); cJSON_Delete(root); printf("%s\n",out); free(out); /* Print to text, Delete the cJSON, print it, release the string. */
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/* Our "days of the week" array: */
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const char *strings[7]={"Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"};
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@ -142,7 +142,7 @@ int main (int argc, const char * argv[]) {
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doit(text4);
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doit(text5);
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/* Parse standard testfiles:
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/* Parse standard testfiles: */
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/* dofile("../../tests/test1"); */
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/* dofile("../../tests/test2"); */
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/* dofile("../../tests/test3"); */
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