How do I dynamically allocate memory to read a .txt file using the strdup function in C

Question

I have a function to dynamically allocate and read a .txt file in C. However according to my assignment instructions the reading of the file should use strdup and not malloc to handle the dynamic memory allocation. I have tried tinkering with the strdup function to get it working, but I have yet to succeed. Here is the current working code using malloc. (NOTE: for my project I am reading 2 .txt files hence why in the main there are two of everything. Putting this to avoid any confusion.)

EDIT 1: using #include sys/stat.h for the stat struct

EDIT 2: Since there are lots of people asking, I am required to use strdup for the dynamic memory allocation. I will not show the instructions but it is explicitly demanded.

//Function that reads .txt input files
char* readInputFile(FILE* targetFile, struct stat stringBuffer)
{           
    char *tempString=malloc(stringBuffer.st_size+1);      
    fread(tempString, 1, stringBuffer.st_size, targetFile);     
    tempString[stringBuffer.st_size] = '\0';     
    fclose(targetFile);     
    return tempString;
}

int main(int argc, char *argv[])
{ 
    struct stat stringBuffer1; 
    struct stat stringBuffer2;
    stat(argv[1], &stringBuffer1); 
    stat(argv[2], &stringBuffer2); 
    FILE *wordListFile1 = NULL, *wordListFile2 = NULL, *outputFile = NULL; 
    wordListFile1=fopen(argv[1], "r");
    wordListFile2=fopen(argv[2], "r");
    char* fileString1;
    char* fileString2;
    fileString1 = readInputFile(wordListFile1,stringBuffer1);
    fileString2 = readInputFile(wordListFile2,stringBuffer2);
    ...
}

Then explain the problem. Why can you not read the file into a stack buffer and then strdup() that into tempString? — Martin James, Jan 18 '20 at 17:46
@Martin James If that is a method that works I would be willing to try. I am just do not know how to do it. The problem is that I need to use strdup instead of malloc, even if the current works preforms what I want correctly. — DegaClaw, Jan 18 '20 at 17:59
You are probably overthinking your assignment, which in all probability calls for reading your files word by word or line by line. — n. m. could be an AI, Jan 18 '20 at 18:14
@MartinJames stat allows to takes the file-info in the stat struct. In his code, he uses the st_size struct member which represents the size of the file. With that he can tells to fread to read all of the file in one time. — naguam, Jan 18 '20 at 18:21
Unfortunately the assignment specifically wants me dynamically allocate using strdup. I actually have the rest of the assignment done already. It is possible I will not lose any points since it works but I need to be sure. — DegaClaw, Jan 18 '20 at 19:00

How do I dynamically allocate memory to read a .txt file using the strdup function in C

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