漢のUNIX JSON データを扱うJanssonライブラリ（Vol.55掲載）
著者：後藤 大地
C言語のJSON用ライブラリ「Jansson」の使い方を紹介する。Janssonライブラリは、使い方がかなり直感的で扱いやすい。C言語でJSONデータを扱いたいのなら最初に使っておきたいものだ。
記事本文掲載のシェルスクリプトマガジンvol.55は以下のリンク先でご購入できます。
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{ "Image": { "Width": 800, "Height": 600, "Title": "View from 15th Floor", "Thumbnail": { "Url": "http://www.example.com/image/481989943", "Height": 125, "Width": 100 }, "Animated" : false, "IDs": [116, 943, 234, 38793] } } |
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[ { "precision": "zip", "Latitude": 37.7668, "Longitude": -122.3959, "Address": "", "City": "SAN FRANCISCO", "State": "CA", "Zip": "94107", "Country": "US" }, { "precision": "zip", "Latitude": 37.371991, "Longitude": -122.026020, "Address": "", "City": "SUNNYVALE", "State": "CA", "Zip": "94085", "Country": "US" } ] |
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{"Image":{"Width":800,"Height":600,"Title":"View from 15th Floor","Thumbnail":{"Url":"http://www.example.com/image/481989943","Height":125,"Width":100},"Animated":false,"IDs":[116,943,234,38793]}} |
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[{"precision":"zip","Latitude":37.7668,"Longitude":-122.3959,"Address":"","City":"SAN FRANCISCO","State":"CA","Zip":"94107","Country":"US"},{"precision":"zip","Latitude":37.371991,"Longitude":-122.026020,"Address":"","City":"SUNNYVALE","State":"CA","Zip":"94085","Country":"US"}] |
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#include <stdio.h> #include <stdlib.h> #include <jansson.h> void print_json_aux(json_t *element, int indent); const char *json_plural(int count) { return count == 1 ? "" : "s"; } void print_json_indent(int indent) { int i; for (i = 0; i < indent; i++) { putchar(' '); } } void print_json_object(json_t *element, int indent) { size_t size; const char *key; json_t *value; print_json_indent(indent); size = json_object_size(element); printf("JSON Object of %ld pair%s:\n", size, json_plural(size)); json_object_foreach(element, key, value) { print_json_indent(indent + 2); printf("JSON Key: \"%s\"\n", key); print_json_aux(value, indent + 2); } } void print_json_array(json_t *element, int indent) { size_t i; size_t size = json_array_size(element); print_json_indent(indent); printf("JSON Array of %ld element%s:\n", size, json_plural(size)); for (i = 0; i < size; i++) { print_json_aux(json_array_get(element, i), indent + 2); } } void print_json_string(json_t *element, int indent) { print_json_indent(indent); printf("JSON String: \"%s\"\n", json_string_value(element)); } void print_json_integer(json_t *element, int indent) { print_json_indent(indent); printf("JSON Integer: \"%" JSON_INTEGER_FORMAT "\"\n", json_integer_value(element)); } void print_json_real(json_t *element, int indent) { print_json_indent(indent); printf("JSON Real: %f\n", json_real_value(element)); } void print_json_true(json_t *element, int indent) { (void)element; print_json_indent(indent); printf("JSON True\n"); } void print_json_false(json_t *element, int indent) { (void)element; print_json_indent(indent); printf("JSON False\n"); } void print_json_null(json_t *element, int indent) { (void)element; print_json_indent(indent); printf("JSON Null\n"); } void print_json_aux(json_t *element, int indent) { switch (json_typeof(element)) { case JSON_OBJECT: print_json_object(element, indent); break; case JSON_ARRAY: print_json_array(element, indent); break; case JSON_STRING: print_json_string(element, indent); break; case JSON_INTEGER: print_json_integer(element, indent); break; case JSON_REAL: print_json_real(element, indent); break; case JSON_TRUE: print_json_true(element, indent); break; case JSON_FALSE: print_json_false(element, indent); break; case JSON_NULL: print_json_null(element, indent); break; default: fprintf(stderr, "unrecognized JSON type %d\n", json_typeof(element)); } } void print_json(json_t *root) { print_json_aux(root, 0); } json_t *load_json(const char *text) { json_t *root; json_error_t error; root = json_loads(text, 0, &error); if (root) { return root; } else { fprintf(stderr, "json error on line %d: %s\n", error.line, error.text); return (json_t *)0; } } char *read_line(char *line, int max_chars) { printf("Type some JSON > "); fflush(stdout); return fgets(line, max_chars, stdin); } int main(int argc, char *argv[]) { char line[4096]; if (argc != 1) { fprintf(stderr, "Usage: %s\n", argv[0]); exit(-1); } while (read_line(line, 4096) != (char *)NULL) { json_t *root = load_json(line); if (root) { print_json(root); json_decref(root); } } return 0; } |
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#include <stdio.h> #include <stdlib.h> #include <jansson.h> int main(int argc, char *argv[]) { // JSONデータをパース json_error_t error; json_t *root = json_loads(buf, 0, &error); // JSON要素の種類判定 switch (json_typeof(root)) { case JSON_OBJECT: break; case JSON_ARRAY: break; case JSON_STRING: break; case JSON_INTEGER: break; case JSON_REAL: break; case JSON_TRUE: break; case JSON_FALSE: break; case JSON_NULL: break; default: } // JSONデータを印刷 printf("%s\n", json_string_value(element)); printf("%f\n", json_real_value(element)); printf("%lld\n", json_integer_value(element)); // 配列処理 int index; json_t *value; json_array_foreach(element, index, value) { printf("%d\n", index); ...value... } // オブジェクト処理 const char *key; json_t *value; json_object_foreach(element, key, value) { printf("%s\n", key); ...value... } // メモリー解放 json_decref(root); return 0; } |
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#include <unistd.h> #include <fcntl.h> #include <stdio.h> #include <stdlib.h> #include <jansson.h> void print(json_t *element, int indent) { const char *key; json_t *value; int index; #define INDENT \ for (int i = 0; i < indent; i++) \ putchar(' '); switch (json_typeof(element)) { case JSON_OBJECT: putchar('\n'); json_object_foreach(element, key, value) { INDENT printf("%s: ", key); print(value, 1+indent); } break; case JSON_ARRAY: putchar('\n'); json_array_foreach(element, index, value) { INDENT printf("%d: ", index); print(value, 1+indent); } break; case JSON_STRING: printf("%s\n", json_string_value(element)); break; case JSON_INTEGER: printf("%lld\n", json_integer_value(element)); break; case JSON_REAL: printf("%f\n", json_real_value(element)); break; case JSON_TRUE: printf("true\n"); break; case JSON_FALSE: printf("false\n"); break; case JSON_NULL: printf("null\n"); break; } } int main(int argc, char *argv[]) { char buf[1024 * 1024]; int fd = open(argv[1], O_RDONLY); read(fd, buf, 1024 * 1024 - 1); // JSONデータをパース json_error_t error; json_t *root = json_loads(buf, 0, &error); // JSONデータをトラバースしながら印刷 print(root, 0); // JSONメモリー解放 json_decref(root); close(fd); return 0; } |