c - 读取文本文件的函数

Question

很难说出这里问的是什么。这个问题是含糊的、模糊的、不完整的、过于宽泛的或修辞性的，无法以目前的形式得到合理的回答。如需帮助澄清此问题以便重新打开它， visit the help center 。

已关闭 10 年前。

我想在 C 编程中拥有一个用户定义的函数，其中该函数将从文件返回文本，并且文件名通过该函数的参数传递给该函数。谢谢。

这是因为我需要将文本附加到变量中。我如何为此修改以下代码。这就是我尝试执行此操作的方法，但现在出现很多错误。

example1.c: In function ‘readfile’:
example1.c:47:5: warning: passing argument 1 of ‘fopen’ makes pointer from integer without a cast [enabled by default]
/usr/include/stdio.h:273:14: note: expected ‘const char * __restrict__’ but argument is of type ‘int’
example1.c:48:5: warning: implicit declaration of function ‘exit’ [-Wimplicit-function-declaration]
example1.c:48:52: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default]
example1.c:56:5: warning: implicit declaration of function ‘malloc’ [-Wimplicit-function-declaration]
example1.c:56:22: warning: incompatible implicit declaration of built-in function ‘malloc’ [enabled by default]
example1.c:57:57: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default]
example1.c:61:59: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default]
example1.c:65:2: warning: return makes integer from pointer without a cast [enabled by default]
example1.c:68:5: warning: implicit declaration of function ‘free’ [-Wimplicit-function-declaration]
example1.c:68:5: warning: incompatible implicit declaration of built-in function ‘free’ [enabled by default]
example1.c: At top level:
example1.c:71:30: warning: initialization makes pointer from integer without a cast [enabled by default]
example1.c:71:1: error: initializer element is not constant

请帮忙。

char readfile (fname) {
    FILE * pFile;
    long lSize;
    char * buffer;
    size_t result;

    pFile = fopen ( fname , "rb" );
    if (pFile==NULL) {fputs ("File error",stderr); exit (1);}

    fseek (pFile , 0 , SEEK_END);
    lSize = ftell (pFile);
    rewind (pFile);

    buffer = (char*) malloc (sizeof(char)*lSize);
    if (buffer == NULL) {fputs ("Memory error",stderr); exit (2);}

    result = fread (buffer,1,lSize,pFile);
    if (result != lSize) {fputs ("Reading error",stderr); exit (3);}

    return buffer;
    fclose (pFile);
    free (buffer);
}
AC_ALPHABET_t * input_text = readfile("infile");

Answer 1

通过一些研究，这确实应该很容易做到，但我修改了你的程序，使其具有一个返回给定文件名的字符串的函数。我想这不是最简单、最好或最正确的方法，但您要求修改您的程序。

#include <stdio.h>
#include <stdlib.h>

char *read_from_file(const char *filename)
{
    long int size = 0;
    FILE *file = fopen(filename, "r");
    
    if(!file) {
        fputs("File error.\n", stderr);
        return NULL;
    }

    fseek(file, 0, SEEK_END);
    size = ftell(file);
    rewind(file);

    char *result = (char *) malloc(size);
    if(!result) {
        fputs("Memory error.\n", stderr);
        fclose(file);
        return NULL;
    }

    if(fread(result, 1, size, file) != size) {
        fputs("Read error.\n", stderr);
        fclose(file);
        return NULL;
    }

    fclose(file);
    return result;
}

int main(int argc, char **argv) 
{
    if(argc < 2) {
        fputs("Need an argument.\n", stderr);
        return -1;
    }

    char *result = read_from_file(argv[1]);

    if(!result) return -1;

    fputs(result, stdout);
    free(result);

    return 0;
}               

示例运行:

[michael@michael-desktop ~]$ echo "hello world" > some_file.txt
[michael@michael-desktop ~]$ ./test some_file.txt
hello world
[michael@michael-desktop ~]$ 

如果需要，我可以评论程序，但查找函数引用可能就足够了。