{"id":4476,"date":"2022-08-23T01:59:17","date_gmt":"2022-08-22T20:29:17","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-problem-of-a-string-read-in-function-system-probably-due-to-a-bad-malloc-closed\/"},"modified":"2022-08-23T01:59:17","modified_gmt":"2022-08-22T20:29:17","slug":"solved-problem-of-a-string-read-in-function-system-probably-due-to-a-bad-malloc-closed","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-problem-of-a-string-read-in-function-system-probably-due-to-a-bad-malloc-closed\/","title":{"rendered":"[Solved] Problem of a string read in function system() (probably due to a bad malloc) [closed]"},"content":{"rendered":"

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chain1 = (char *) malloc(5*sizeof(char*) + 1);\n<\/code><\/pre>\n
This will allocate enough space for five character pointers<\/em> plus an extra byte. A pointer is not the same as a character, it tends to be either four or eight bytes currently but can actually be any size. You probably want sizeof(char)<\/code> but, since that’s always 1, you can just ignore it in multiplications.<\/p>\n
You probably also want a number higher than five since that’s not even enough to store your fixed prefix.<\/p>\n
In addition, the current content<\/em> of that allocated block will be arbitrary so strcat<\/code> is not<\/em> the first operation you should be performing on it (since that requires a valid C string).<\/p>\n
This is almost certainly<\/em> the cause of your “string starts with rubbish” problem. A strcpy<\/code> would be better as the first operation, or just use sprintf<\/code> to do the whole thing at once, rather than a strcpy\/multiple-strcat<\/code> sequence.<\/p>\n
And, finally, a command passed to system<\/code> does not need a trailing newline.<\/p>\n
A better method may be something like:<\/p>\n
static const char prefix[] = \"cp mediaPlayer.exe \";\nchar *chain1 = malloc(sizeof(prefix) + strlen(actual->chain));\nif (chain1 != NULL) {\n    sprintf(chain1, \"%s%s\", prefix, actual1->chain);\n}\n<\/code><\/pre>\n
Space for the terminating \\0<\/code> is accounted for my using sizeof<\/code> on the string rather than strlen<\/code>. The former includes space for the terminator. And note the check for a failed malloc<\/code>, this is something you should always<\/em> do if you want robust code. I shouldn’t need to mention that, should chain1<\/code> end up being NULL<\/code> at the end of this code block, you should not<\/em> pass it to system<\/code>.<\/p>\n<\/p><\/div>\n
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solved Problem of a string read in function system() (probably due to a bad malloc) [closed] <\/p>\n","protected":false},"excerpt":{"rendered":"
[ad_1] chain1 = (char *) malloc(5*sizeof(char*) + 1); This will allocate enough space for five character pointers plus an extra byte. A pointer is not the same as a character, it tends to be either four or eight bytes currently but can actually be any size. You probably want sizeof(char) but, since that’s always 1, … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[320],"tags":[324,386,880,362,879],"class_list":["post-4476","post","type-post","status-publish","format-standard","hentry","category-solved","tag-c","tag-malloc","tag-strcat","tag-string","tag-system"],"yoast_head":"\n[Solved] Problem of a string read in function system() (probably due to a bad malloc) [closed] - JassWeb<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/jassweb.com\/solved\/solved-problem-of-a-string-read-in-function-system-probably-due-to-a-bad-malloc-closed\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"[Solved] Problem of a string read in function system() (probably due to a bad malloc) [closed] - JassWeb\" \/>\n<meta property=\"og:description\" content=\"[ad_1] chain1 = (char *) malloc(5*sizeof(char*) + 1); This will allocate enough space for five character pointers plus an extra byte. 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