如何正确释放C语言中分配的内存

Question

我有两个函数。在find_host(...)中，我为main函数中的free分配了内存。

char* find_host(char* filename){
    char *x = malloc(20);
    sprintf(x, filename);
    const char* t = "10";
    int len = (int) strcspn(filename, t);
    x[len] = '';
    return ++x;
}
int main(){
    char *filename = "/CERN0/out_79.MERGE";
    char *word = find_host(filename);
    free(word);
    return 0;
}

但free(word)给了我:

*** Error in `/home/ken/.CLion2016.2/system/cmake/generated/First-6a656bbe/6a656bbe/Debug/First': free(): invalid pointer: 0x00000000008b1011 ***
======= Backtrace: =========
/lib/x86_64-linux-gnu/libc.so.6(+0x77725)[0x7f926862f725]
/lib/x86_64-linux-gnu/libc.so.6(+0x7ff4a)[0x7f9268637f4a]
/lib/x86_64-linux-gnu/libc.so.6(cfree+0x4c)[0x7f926863babc]
/home/ken/.CLion2016.2/system/cmake/generated/First-6a656bbe/6a656bbe/Debug/First[0x4006e9]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf0)[0x7f92685d8830]
/home/ken/.CLion2016.2/system/cmake/generated/First-6a656bbe/6a656bbe/Debug/First[0x400579]
======= Memory map: ========

如何正确使用free内存?

Answer 1

只能在调用malloc()及其同类函数实际返回的指针值上调用free()。由于希望跳过初始字符，因此可以在填充缓冲区时跳过，而不是返回修改后的指针。

char* find_host(char* filename){
    size_t sz = strlen(filename);
    char *x = malloc(sz);
    snprintf(x, sz, "%s", filename + 1);
    const char* t = "10";
    int len = (int) strcspn(filename, t);
    x[len] = '';
    return x;
}