c - 为什么第二个 malloc 在这种情况下会失败？

Question

我目前正在处理一段代码，我们正在解析文件并使用不同的函数。通过printf调用调试，我发现第二次malloc调用时出现内存错误。什么可能导致第二个malloc在这个粗糙的骨架中失败？

struct example {
    char *myChar;
    int myInt;
};

struct example *doThing(FILE *file) {
    struct example *myToken = (struct example *)malloc(sizeof(struct example));
    char buffer[32] = "";

    // other stuff

    if (strncmp(buffer, "random", 6) == 0) {
        strncpy(myToken->myChar, buffer, 6);
        myToken->tokenid = 1;
        return myToken;
    }

    return NULL; 
}

struct example *doThing2(FILE *file) {
    struct example *myOtherToken = (struct example *)malloc(sizeof(struct example));
    // other stuff
    return myOtherToken;
}

int main() {
    FILE *ofp = fopen("thefile.txt", "r");
    struct example *token1, *token2;

    token1 = doThing(ofp);
    token2 = doThing2(ofp);

    // other stuff

    free(token1);
    free(token2);
    return 0;
}

标签： cpointersstructmalloc

Answer 1

您正面临内存泄漏。按照以下两个示例之一更正您的代码

是的，正如@Eugene_Sh 所提到的，您应该分配内存myToken->myChar并且不要忘记在释放 myToken 之前释放它

样品 1

struct example* doThing(FILE *file) {

    char buffer[32] = "";

    // other stuff

    if (strncmp(buffer, "random", 6) == 0) {

        struct example *myToken = (struct example *) malloc(sizeof(struct example));

        myToken ->myChar= malloc(7);
        strncpy(myToken ->myChar, buffer, 6);
        myToken ->myChar[6]=0;
        myToken->tokenid = 1;
        return myToken;
    }

    return NULL; 
}

样品 2

struct example* doThing(FILE *file) {
    struct example *myToken = (struct example *) malloc(sizeof(struct example));
    char buffer[32] = "";

    // other stuff

    if (strncmp(buffer, "random", 6) == 0) {


        myToken ->myChar= malloc(7);
        strncpy(myToken ->myChar, buffer, 6);
        myToken ->myChar[6]=0;
        myToken->tokenid = 1;
        return myToken;
    }
    free(myToken );
    return NULL; 
}