C - 段错误(核心转储)，从文件中读取前 N 个字节

Question

我编写了一些代码来从二进制文件中读取第一个 pos 字节并将其写入另一个文件中。结果我运行时遇到了段错误。这是代码:

void outputUntillPos(const char * inFileName, const char * outFileName, int pos) {
FILE * inFile = fopen(inFileName, "r");
FILE * outFile = fopen(outFileName, "aw");

char buf[1024];
int read = 0;
int remain = pos;

do {
    if(remain <= 1024) {
        read = fread(buf, 1, pos, inFile);
    } else {
        read = fread(buf, 1, 1024, inFile);
    }

    remain -= read;
    fwrite(buf, 1, read, outFile);
    memset(buf, 0, 1024);
} while(remain > 0);
}

我是否在这里进行了超出范围的操作？

编辑:感谢所有帮助，这是编辑后的代码。

void outputUntillPos(const char * inFileName, const char * outFileName, int pos) {
FILE * inFile = fopen(inFileName, "r");
FILE * outFile = fopen(outFileName, "aw");

char buf[1024];
int read = 0;
int remain = pos;

if((inFile != NULL) && (outFile != NULL)) {
    do {
        if(remain <= 1024) {
            read = fread(buf, 1, remain, inFile);
        } else {
            read = fread(buf, 1, 1024, inFile);
        }

        remain -= read;
        fwrite(buf, 1, read, outFile);
        memset(buf, 0, 1024);
    } while(remain > 0 && read > 0);
}

fclose(inFile);
fclose(outFile);
}

Answer 1

当 remain 变为 <= 1024 并且输入 block 的 if 部分时，您将读取 pos 字节，如果大于 1024 时将写入缓冲区末尾。这就是导致段错误的原因。

您想在此处使用remain:

if(remain <= 1024) {
    read = fread(buf, 1, remain, inFile);
} else {
    read = fread(buf, 1, 1024, inFile);
}

另外，在返回之前请务必检查 fopen 的返回值，以及 fclose(inFile) 和 fclose(outFile) .